1. Field of the Invention
The present invention relates to a heat pipe heat recovery unit for unidirectional, but reversible, and temperature controllable transfer of heat between at least two ducts.
2. Description of the Prior Art
The ever-increasing need to conserve energy resources in industrial and habitable environments has generated a large number of possible solutions. Such solutions generally involve the transfer of heat between exhaust and supply ducts in which the warmer fluid of one duct is extracted by means of heat pipes transferred to the fluid flowing through the other duct.
Two concepts advanced in recent years are described in the U.S. Pat. Nos. 3,788,388 and 3,980,129. The latter patent is concerned with reducing frost build-up at the exit end of the exhaust-duct heat exchanger. The heat pipes are disposed horizontally within the heat exchanger which is rotated about an axis so that, when ice forms at the end of the warm air exhaust nearest the cold outside environment, the heat exchanger may be turned to 180.degree. about its axis so that warm exhaust air impinges directly on the frosted heat pipes. In U.S. Pat. No. 3,788,388 heat transfer between ducts is bi-directional which is claimed to occur as a result of the liquid phase of the working fluid being normally free-standing along substantially the entire length of the heat pipes, with a substantial vapor space also substantially along the entire length of the heat pipes. Tilt is induced solely to limit the amount of heat transferred from the air stream in one duct to the air stream in the other duct by reducing the effective length of the heat pipes and, therefore, the overall efficiency of the thermal transfer unit.